Tile Underlayment: Be Prepared

   A finished surface is the only part of installation that people see once a project is complete. However, the unseen substrate must be properly prepared to provide the best bonding surface and create a stable setting surface. These steps help guarantee that a finished surface stands the test of time.
   Surface-preparation materials must be compatible with the conditions on the project site, and with the requirements of the floor coverings being applied. They must also be compatible with each other in order to maintain the integrity of the installation system.
   Ensuring this quality requires three things:
   1) An accurate assessment of the surface to be tiled;
   2) The careful selection of surface-preparation products—backerboards, patching and leveling underlayments, membrane applications and sound-reduction materials; and
   3) The proper technique to assure the integrity and longevity of the installation. 
  
A SOLID CHOICE
   A stable, porous surface is essential in order to create a sufficient bond. In new construction, most floors or counters to be tiled will be either plywood or concrete; walls or tub surrounds will probably be greenboard, drywall or studs.
   Concrete, if it’s level and free of cracks, is an ideal substrate for laying tile. Plywood and greenboard are too dimensionally unstable – and susceptible to water damage – to serve as untreated substrates, and they don’t provide a proper surface for bonding. Their movement will most likely lead to severe cracking over time, and the porosity means that absorbed water from atmospheric conditions and installation materials will cause warping. 
   Backerboards help protect against long-term moisture damage and provide an appropriate surface for adequate bonding. For installations over plywood subfloors, countertops or walls, backerboards provide strong, rigid surfaces for tile application.
   There are three types of backerboards on the market today. Cementitious, the oldest and most-popular, is a cement board wrapped in a fiberglass mesh coating. It offers exceptional durability and protection against moisture, and is ideal for both interior and exterior use in commercial and residential projects.
   In the past several years, fiber cement backerboards have grown in popularity for interior installations, largely because they are lighter in weight and cleaner to work with. Recently, the third generation of backerboard technology entered the market, offering ultra-light weight along with comparable strength and workability. These new ultra light weight backerboards have a lightweight core encased in a cementitious slurry coating. They are exceptionally easy to carry and work with, and offer strength and water resistance that rival traditional cementitious boards. 
   Backerboards typically are offered in two thicknesses: 1/2” and 1/4” The thinner profile of 1/4” boards is usually preferred for counters and floors, because construction heights are lower and transitions from tile to carpet are easier to manage. Boards with a 1/2” thickness are ideal for wall or countertop use.
   Once the backerboard is selected, it can be applied to the surface easily using nails or backerboard screws. For a floor installation, a bed of thin set should be laid first to create a level bed, and the backerboard can then be screwed or nailed down. For wall installations, backerboard should be affixed directly to the studs.
   If the area to be tiled is a shower or tub surround, a moisture barrier will be necessary before applying backerboard. Roofing felt is the most-common material for this purpose; it should be cut to fit the space, and then stapled or nailed to the studs prior to installing the backerboard.
  
LEVELING, BARRIERS AND SOUND
   Regardless of the backerboard, however, a surface to be tiled needs to be flat.
   For uneven or cracked surfaces, there are several patching and leveling products available that can be mixed and poured like cement, curing to a finished level surface that’s ready to tile. Some are also available in a “rapid setting formula”, meaning fast curing time, which can be crucial for commercial or high traffic projects. 
   The best leveling products are ASTM C627 rated for use in ceramic-tile installations over wood subfloors; these also earn an “extra heavy” rating for use in commercial environments such as food plants, dairies, breweries and kitchens.
   After making sure the surface is flat, installers need to determine if a waterproofing membrane or soundproofing material will be necessary.
   For areas with heavy, constant water exposure (such as showers, exterior decks and patios) an elastomeric waterproofing and anti-fracture membrane creates a protective division between the substrate and tiles, providing protection from crack transmission and potential moisture damage. Membranes certified by IAPMO/Uniform Plumbing Code File No. 4244 are preferred, meaning that they are reliable enough to serve in high-moisture applications such as shower-pan liners.
   The waterproofing membrane should be applied according to the manufacturer’s instructions – some can be applied easily with a roller, trowel or sprayer, while others require mesh fabric as part of their system.  It can be applied over concrete, backerboards, or exterior-grade plywood substrates, and usually requires two coats. If using a roller, the first coat should be applied in long, straight strokes, with the second coat applied in the same manner but at a 90° angle for maximum protection.
   An anti-fracture membrane’s rubbery flexibility also reduces the effects on the tiles from natural crack shifts that may occur in the substrate over time. In a completely rigid flooring system, these shifts can reveal themselves through unsightly cracks on the tile surface, meaning costly repairs.
   Water may not pop up as a concern, but sound control could  – especially for apartments, condominiums, hotels and commercial buildings. Sound transmission is more of an issue in tiled environments today, due to increased enforcement of related building codes and a trend toward quieter buildings.
   These shifts in acoustic considerations may cause some people to question the use of tile, but the application of new sound-reduction mat underlayments simplifies the sound-control process and keeps tile on the list of preferred floor-covering options. Each of these products will improve the Impact Insulation Class (IIC) ratings, the industry standard measurement for sound transmission, according to manufacturer specifications. 
   Application methods for each material will vary, but sound-reduction mat underlayments are very thin (meaning that they have a minimal effect on construction heights) and provide an exceptional bonding surface for both substrate and tile. A layer of thin-set mortar is applied to the substrate (either backerboard or concrete), and the mat is rolled down directly onto it.  The surface is now ready for the application of thin-set mortar and tile.
  
WELL PREPARED, WELL DONE
   When the project is complete, all that will be seen of the work is the beautiful tile installation. That tile, however, will only remain effective and attractive if it is laid on a solid, properly prepared surface. Only solid first steps will lead to a successful project that will stand the test of time, beginning with smart product choices and high-quality surface preparation.

Backerboard Basics

Interior installations
• Cementitious
• Fiber cement
• Ultra light weight

Exterior installations
• Cementitious

Walls
• Cementitious
• Fiber cement

Floors
• Cementitious (1/4”)
• Fiber cement (1//4”)
• Ultra light weight (1/4”)

Tubs, Showers and Spas
• Cementitious
• Ultra light weight

Countertops
• Cementitious
• Fiber cement
• Ultra light weight

This article first appeared in the June 2004 print edition of Stone Business. ©2004 Western Business Media Inc.